An organic thin-film solar cell is a solar cell that uses an organic thin-film semiconductor formed by combining a conductive polymer, a fullerene, and the like. Compared with a solar cell formed mainly with an inorganic material such as silicon, CIGS, or CdTe, an organic thin-film solar cell can be produced by a simple process like application or printing of a photoelectric conversion film. The production costs of organic thin-film solar cells can be lower accordingly. On the other hand, the photoelectric conversion efficiency and the service life of an organic thin-film solar cell are lower and shorter than those of a conventional inorganic solar cell. The same applies to thin-film solar cells using a semiconductor material having a perovskite structure.
In a typical organic thin-film solar cell module, a transparent first electrode is formed on a transparent substrate, an organic photoelectric conversion film including an active layer (a photoelectric conversion layer) is formed on the transparent electrode, a second electrode (also called a back electrode) is formed on the organic photoelectric conversion film, and a supporting substrate (also called a back substrate) is formed on the second electrode via a resin layer serving as an adhesive.
The photoelectric conversion efficiency of an organic thin-film solar cell drops during use, and the durability of the organic thin-film solar cell becomes poorer. In an organic thin-film solar cell module, one of the reasons that the photoelectric conversion efficiency drops during use is that the active layer made of an organic material has a low resistance to moisture. To prevent degradation of the active layer due to moisture and increase durability, the transparent substrate and the supporting substrate are bonded to each other with a sealing agent at end portions according to a known technique. This sealing agent has a role to prevent moisture infiltration through end portions. However, the distance from the power generating cells to the sealing agent and the width of the sealing agent add to the regions that do not contribute to power generation (such regions are referred to as the no-power generating regions). Although the amount of infiltrating moisture can be reduced with a thinner resin layer serving as an adhesive, the adhesion strength between the transparent substrate and the back substrate becomes lower, resulting in a lower module strength.